1. Field of the Invention
The present invention relates to an information storage carrier for storing intelligence information along a path on the carrier extending from an upstream location to a downstream location, and more particularly, to a video disc containing prerecorded intelligence information in the form of a series of television picture frames with each series of frames being duplicated on the surface of the carrier at at least two locations. By duplicating a program of video information on the storage member, the player playing back the prerecorded information can search for and play back a second, or further, duplicate version of the program upon detecting improper reproduction of the information played back from the first program version, or upon failure to detect the presence of the first program.
2. Description of the Prior Art
Video discs structures are described by John Winslow in his patent application entitled "Mastering Machine," filed Mar. 27, 1978, Ser. No. 890,407, now U.S. Pat. No. 4,225,873 issued Sept. 30, 1980, and assigned to the assignee of the present invention.
A video disc structure is also described by John Holmes in his patent application entitled "Video Disc Composition and Method of Molding" filed Aug. 28, 1978, Ser No. 937,221, and assigned to the assignee of the present invention.
Other prior art references which pertain to the field of this invention include: U.S. Pat. No. 4,228,326 issued Oct. 14, 1980 to Dakin, et al which discloses a video disc rotating at a constant linear velocity relative to a read head for the disc and teaches the use of "concentric circles" track format; U.S. Pat. No. 4,161,753 issued July 17, 1979 to Bailey et al disclosing the interlacing of data for picture frames on the same track and teaches the formatting of a video disc rotating at a constant angular velocity relative to its read head.
Each of the prior art video disc structures bear information in the form of concentric circles or a spiral track extending from an upstream start position to a downstream end position. The disc is played by causing a read head to progress along the concentric circular or spiral path from the upstream to downstream positions and to play out a complete program as it progresses from start to finish. If the length of the program recorded on the video disc were shorter than the available time on the disc surface, the remaining unrecorded disc area would be left blank.
Upon playing back the prerecorded program, the read head of the player can encounter defects or blemishes on the surface of the disc, thereby destroying the synchronization and/or color registration or causing picture loss often accompanied by a noisy (snowy) interval. The defect or blemish on the disc could be the result of imperfect manufacturing processes or caused by mishandling of the disc by the user. While the quality control of video discs produced for distribution are closely monitored, and while present technology applied in the production of the video disc provides a disc which is reasonably insensitive to handling, 100% quality control is not achievable, and inadvertent dropping or scratching of the disc surface by the user is not uncommon. In the past, in order to improve yield in the recovery of information, and recognizing the fixed limits of disc production yield, several disc players were loaded with similar discs, and a video/audio (or r.f.) switcher would select one of the player outputs, and upon detection of an error would switch to another player. Obviously, this is an expensive solution to the problem and furthermore does not improve signal recovery probability in areas of the disc that are defective due to certain systematic production irregularities. A scratch or dust particle in a disc stamper, for example, could cause the same defect in each disc produced by that machine. Thus, no number of redundant players could serve to eliminate signal loss at such a defect location. The present invention, on the other hand, both eliminates the need for redundant players and eliminates the effects of systematic production irregularities, since the redundancy of information lies in different portions of the disc. Accordingly, there is a need in the art for a video disc having a higher production yield for a given recorded program, yet having the ability to avoid or significantly reduce the problems associated with a defective disc passing through quality control or with improper handling by the ultimate user. The present invention is directed to a formatting technique for overcoming the disadvantages associated with the aforementioned problems.